On Mon, 8 Jun 1998 21:47:36 +0200,
Hauke Fath <hauke@Espresso.Rhein-Neckar.DE> wrote:
> At 2:19 Uhr +0200 08.06.1998, Ken Nakata wrote:
> >On Mon, 8 Jun 1998 00:30:23 +0200,
> >Hauke Fath <hauke@Espresso.Rhein-Neckar.DE> wrote:
> 
> >> The iwm floppy driver is known to work on the SE/30, the IIsi/ci and the
> >> Q700. It does NOT work on IOP machines (IIfx, Q900/950, Q840AV, Q660AV?)
> >> due to different hardware.
> >
> >The AV's don't have an IOP, but they don't have a SWIM chip, either.
> 
> I used the term IOP somewhat loosely in the sense of "doing GCR decoding
> on-chip". In fact, I have just re-read a set of snippets from technotes
> Apple has online. They said about the 840AV's floppy controller...

You mean IOP *not* "doing GCR decoding on-chip"?  The New Age (AV's
floppy controller chip) just doesn't seem to have hardware GCR
encoder/decoder, from what I can read below.

> ---------------------------------------------------------------------------
> >[Macintosh AV Series: Floppy Drive Performance (5/94)]
> >
> >This microprocessor (the new integrated floppy controller), while taking over
> >all of the timing-critical floppy control functions, does not have the
> >computational
> >speed of the main processor, or the speed of the 68000 used in original
> >Macintosh systems. The result is that for GCR formatted disks (800K), the
> >additional computation used in GCR coding and decoding makes accesses to and
> >from an 800K floppy slower than on previous macintosh systems. Our tests show
> >that it usually takes about 50% longer to read and write to an 800K floppy on
> >the AV systems as compared to other Macintosh systems. Currently, there are no
> >plans to change the floppy controller for an increase in performance. The
> >performance of the floppy drive in 1.44M mode is comparable to other
> >Macintosh systems.
> >
> >The 800K read/write performance is a compromise in order to provide the
> >additional functionality of those products based on the current
> >technology, cost, and time to market constraints.

I tried to get my hands on whatever on-line docs available on AV Macs,
but I anyhow missed this one...  The New Age on my Q840AV's logic
board is in fact an NEC uPD72070.  That's why I called their local
branch for a copy of datasheet.  Looks like MFM format (1.4M) will be
much easier to implement than GCR formats on AV's.

Ken